Market demand for smaller, lighter, and more powerful electronic devices has driven the development of more compact packages having increased functionality. The market demand has spurred semiconductor packaging technologies in the areas of fine pitch ball grid arrays (FBGA), chip-scale packages (CSP), wafer-level packaging (WLP), multi-chip module (MCM) technology, and stacked die packaging. MCM technologies provide multiple semiconductor chips functionally assembled in one package, such as multiple stacked die in a CSP or multiple stacked die on a BGA.
A die package includes one or more semiconductor chips mounted to a carrier and electrical connectors attached between the carrier and the chip. The electrical connectors include wires, clips, etc., that electrically connect the chip to other electronic devices. Ball bonding is one way of bonding the electrical connectors to the chip. Ball bonding uses a combination of heat, pressure, and ultrasonic energy to weld the connectors onto the chip.
Copper electrical connectors are relatively inexpensive and have superior electrical properties compared to gold or aluminum connectors. However, the melting point of copper is about 1083 degrees Celsius, such that high temperatures and force are used during copper ball bonding. The high force applied during connection of the connector to the chip has the potential to damage the chip. For this reason, ball bonding a copper connector to an active surface of a chip is undesirable. In addition, copper is highly susceptible to oxidation. The use of copper electrical connectors necessitates that some method of preventing oxidation of the copper be employed during bonding. One approach includes purging the atmosphere near the bond site with an inert gas (e.g., nitrogen) to minimize the oxidation of the copper during bonding. Inert gas purging during the electrical connection process is an expensive and an undesirable extra step.
For these and other reasons there is a need for the present invention.